1) Undo setting _debug as synchronized. It was already synchronized inside itself, and adding the wrapper broke getting the correct method name.

2) Import the date methods once.

3) Make date_read sync'able in both directions
1) Fix crash that is triggered by apps not using caching.
2) Don't refresh the GUI when requesting the transfer of unchanged metadata to the device.
1) Put the embedded import statements back
2) Fix syncing not to attempt to sync if either column is bad
3) Make independent syncing of the date read work
Add ability for device to do a version check for syncing.
Merge branch 'master' of https://github.com/cbhaley/calibre